Lateral-line sensors allow new robotic fish to go with the flow

FILOSE robotic fish
Robots with lateral-line sensors are better equipped to deal with flowscape changes. They are able to anticipate upcoming influences and react accordingly. This capability could be particularly valuable to low-inertia, underwater robots.
Professor William Megill
By exploiting biological principles, an international team of roboticists has created a robotic fish capable of navigating flow landscapes. The scientists, whose research has been published in the journal Proceedings of the Royal Society A, claim that this newly developed technology will allow underwater vehicles to use flow to their advantage for the first time.

The robot was created as part of the EU-funded Robotic FIsh LOcomotion and SEnsing (FILOSE) project, and involved scientists from Tallinn University of Technology (TTU), the University of Bath, Riga Technical University (RTU), the University of Verona and the Italian Institute of Technology (IIT). In order to create an artificial fish capable of traversing flow landscapes, or ‘flowscapes’, the team designed and created the world’s first manmade lateral-line sensor. Data collected by this instrument can be used to create detailed pictures of flowscapes, thus enabling the robot to navigate and control its movements in an efficient and reactive manner.

To learn more about the development and potential applications of this new technology, I spoke to participating scientist Professor William Megill, former member of the University of Bath’s Department of Mechanical Engineering. I began by asking how he and his colleagues approached the creation of their flowscape-traversing, robotic fish.

"The lateral-line sensor was actually developed by the Italian group," explained Professor Megill, who is now based at Rhine-Waal University of Applied Sciences. "My team collected biological information from real fish. Our Italian colleagues then designed the lateral-line sensor by drawing upon this information, and they devised a novel manufacturing technique to produce the sensor."

Real fish possess organs that act as natural lateral-line sensors, but until now, there has never been an artificial analogue. Consequently, within contemporary robotics, flow is viewed as a hindrance that prevents vehicles from travelling to their intended destinations. The researchers hope that the technology that they have developed will enable future generations of water-faring robots to actually benefit from flow.

"Consider the tsunamis that have affected Southeast Asia during the last decade," said Professor Megill. "Lots of cars and cows were swept out to sea, yet not many fish were washed up on land. This is because fish are able to anticipate and react to their local flowscape. They are really good at dealing with changes in flow direction. If you were to place one of today’s underwater robots under tsunami conditions, you’d most likely be searching for its parts on the beach. Current robots find it really difficult to go with the flow.

"Robots with lateral-line sensors are better equipped to deal with flowscape changes," he continued. "They are able to anticipate upcoming influences and react accordingly. This capability could be particularly valuable to low-inertia, underwater robots. By employing a concept known as virtual inertia, they can increase their effective inertia – the stiffness of their bodies – in order to deal with flow forces. Essentially, the robots can behave as if they are a lot larger and heavier than they actually are. A tsunami doesn’t bother a whale because a whale is big enough to let flow forces just pass over it. A little fish, however, must ‘pretend’ to be a whale in order to deal with such conditions. These are the principles that we exploited when building our robotic fish."

Tsunamis generate some of the most extreme flow conditions on Earth. Even so, the principles that apply during these events can be extrapolated to more mundane underwater situations, such as when robots have to operate in the nearshore. Lateral-line sensors will allow low-inertia, ‘soft’ robots to maintain stability within dynamic flowscapes, and could even enable them to use flow to their advantage. However, the knowledge gained by the FILOSE team hasn’t been one directional. The scientists’ experiments have also uncovered new information about real fish, as Professor Megill explained.

"You cannot ask a fish detailed questions about the way in which it senses the world," he said. "However, by testing our lateral-line sensor within environments similar to those inhabited by real fish, we were able to sense what a fish might sense under the same conditions. This provided us with an idea of what real fish see; what flow structure looks like to a fish. We didn’t go as far as to explore the brains of real fish, but this is a potential avenue for future research. Researchers, for instance, could attach electrodes to a fish’s nervous system to gauge how it reacts under certain flow conditions."

To conclude our conversation, I enquired about what the FILOSE team intends to do in the future. What are the researchers working on now that they have developed their lateral-line sensor?

"This project has left quite a legacy," Professor Megill replied. "TTU’s Professor Maarja Kruusmaa, the Scientific Coordinator of the FILOSE project, is now exploring the possibility of using soft robots to conduct archaeological work in the Baltic. Our Italian colleagues are pushing on with the development of the lateral-line sensor. They are going to test the instrument with micro air vehicles (MAVs). I am also interested in this possibility. The challenges posed by aerial flowscapes are similar to those faced by our robotic fish. The work that we have so far conducted under FILOSE has opened up a whole host of new research opportunities. It has been a really successful project."

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